Triode oscillator circuit



Sept, 3, 1946; \v/ARELA 2,406,871 I TRIODE OSCILLATOR. CIRCUIT FiledSept. 22, 1941 2 Sheets-Sheet 2 'nwiwron Arlkuzul Varela lur romvsr 7Patented Sept. 3, 1946 UNITED STATES PATENT OFFICE (Granted under theact of March 3, 1883, as amended April 30, 192.8; 37 0. G. 757.)

4 Claims.

This invention relates to radio frequency pulse generators and moreparticularly to self-quenchin oscillator circuits for generating radiofrequency pulses.

Self-quenching oscillator circuits that have been proposed heretoforefor generating radio frequency pulses comprise a conventional oscillatorcircuit, includingan electron discharge device having an anode, cathodeand at least one control electrode interconnected in such a mannor as tocause said device to oscillate. In order to provide the self-quenchingfeature and thus produce radio frequency pulses at the. output of thecircuit, the prior systems utilize resistance means, of a high value,connected in the control electrode path, with suitable capacitance meansshunted across the resistance means. In operation of systems of theforegoing character, when the electron device commences to oscillate,rectified control electrode current is generated which flows to andgradually charges the capacitance means thus producing a graduallyrising self-bias on the control electrode which in turncauses the.

angle during which the anode draws current to gradually decreaseuntilthe point of extinction is reached. The term anode current anglementioned above and referred to hereinafter in the specification and theclaims has reference to the period that the plate of the oscillator tubedraws current with respect to each cycle of excitation voltage appliedto the control grid of the tube.

The foregoing operation produces radio frequency pulses havingasymmetrically shaped envelopes, due to the inherent operatingcharacteristics of the capacitance means. The magnitude of the pulseenvelope is notsubstantially constant throughout any portion thereof,and. the radio frequency voltage magnitude, with respect toan increasein the period of the pulse, gradually becomes less and less as thepointof extinction. is reached. From all practical viewpoints, radiofrequency pulses having pulse envelopes of substantially rectangularsymmetrical shap wherein the magnitude of each pulse envelope remainssubstantially constant throughout a greater portion thereof, and whereinthe magnitude of the envelopes sharply decreases, from "maximum to theextinction point, through a small period of the pulse, has been founddesirable for numerous reasons. As stated above, in operation of theprior systems, the control electrode voltage continually variesthroughout the period of the pulse, such voltage variations not onlyproduces asymmetrical pulse envelopes but also produces a shift in thecarrier frequency. Such frequency modulation is very objectionable sinceit requires a corresponding decrease in receiver selectivity withresulting loss in signal to noise ratio. The desired substantiallyrectangular symmetrical pulse envelopes tend to maintain the carrierfrequency substantially constant throughout the period of the pulses,and also tends to compensate for other frequency variations inthe'carrie'r wave which occur as the operating time of the circuitincreases.

It is therefore an object'of the present invention to provide a novelself-quenching oscillator circuit for generating radio frequency pulseswherein the pulse envelopes are of the aforementioned desired shape."

Another object is to provide a self-quenching oscillator circuitforgeneratin radio frequency pulses wherein the direct current voltageapplied to the oscillator tube or tubes is substantially constantthroughout the principal portion of the pulse.

Another object is to provide a self-quenching radio frequency pulsegenerator wherein the carrier frequency is maintained substantiallyconstant throughout generation of the pulse.

Another object is to provide a self-quenching oscillator circuit forgeneratingradio frequency pulses having pulse envelopes withsubstantially constant magnitude throughout a greater portion thereof,and wherein the magnitude of the envelopes sharply decreases frommaximum to an extinction point, through a small period of the pulse.

Another object is to provide a self-quenching oscillator circuitincluding novel means for generating radio frequency pulses havingsubstantially rectangular pulse envelopes.

Still another object of the present invention is to provide aself-quenching oscillator circuit including an electron discharge devicehaving an anode, cathode and-at least one control electrode and novelmeans connected between the cathode and the control electrode forproducing and controlling a self-bias on the control electrode wherebythe angle during which the anode draws current remains substantiallyconstant throughout a predetermined period of time and thereafterdecreases to a point of extinction throu out a short period the pulse.

Still another object is to provide aself-quenching oscillator circuitfor generating radio frequency pulses having a filter network includedin the circuit for producing substantially rectangular Symmetrical.pulse'envelopes.

Still another object of the invention is to provide an oscillatorcircuit including at least one electron discharge device having ananode, cathode and at least one control electrode, with a filter networkconnected between the cathode and the control electrode for producingand controlling abias on the control electrode in such a manner thatradio frequency pulses having substantially rectangular symmetricalpulse envelopes are formed.

Other objects and features of the inventionwill appear more fully fromthe following detailed description when considered together with theaccompanying drawings which disclose two embodiments of the invention.It is to be expressly understood, however, that the drawings aredesigned for purposes of illustration only and not as a definition ofthe limits of the invention, reference being had to the appended claimfor the latter purpose.

In the drawings, wherein similar reference characters denote similarparts throughout the several views:

Fig. 1 is a diagrammatic showing of a pulse envelope formed uponoperation of the prior systems mentioned heretofore;

Fig. 2 is a schematic showing of a self-quenching oscillator circuit,embodying the principles of the present invention, for generating radiofrequency pulses having substantially rectangular symmetrical pulseenvelopes;

Fig. 3 is a diagrammatic view of a pulse envelope formed upon operationof the system disclosed in Fig. 2, and

Fig. 4 is a schematic showing of another embodiment of the presentinvention.

As shown in Fig. 1 of the drawings, and as mentioned heretofore, theprior self-quenching oscillator circuits for generatin radio frequencypulses produce pulses having asymmetrical pulse envelopes in which themagnitude of the pulse is not substantially constant throughout anyportion of the pulse. Due to the inherent characteristics of thecapacitance means employed in the prior systems, the magnitude of thepulse envelopes gradually decreases, and the rate of such decreasebecomes greater as the time of the pulse increases.

As stated heretofore, it is an object of the present invention toprovide an oscillator circuit for I lator circuit including theaforementioned means i is shown therein having a pair of electrondischarge devices I B and H, such as thermionic tubes ofthe triode type,each of which respectively includes a cathode l2 and I3, an anode l4 andI5 and a control electrode l6 and IT. The cathodes are joined togetherat point I8 and are connected to ground potential at l9, while theanodes are connected together at point and are maintained at a positivepotential with respect to the cathodes. A source of high potential issupplied to points 2| and 22, the former point being connected to theanodes, while the latter is connected to ground potential. The controlelectrodes l6 and I! are connected together at point 23, and the controlelectrodecathode circuit includes suitable resistance means 24, a filternetwork 25, the purpose of which will appear more fully hereinafter, andtransformer 26, serially connected between points 23 and IS.

A source of alternating voltage 21 is applied to transformer 26 forpurpose of synchronization as will also become more apparenthereinafter. The oscillator circuit disclosed herein is a conventionalhigh frequency, push-pull, linear oscillator wherein the lump inductanceand capacity in the plate leads and in the cathode or control electrodeleads are replaced by resonant electrical lines. This type of oscillatorcircuit is capable of producing ultra-high frequency oscillations withhigh stability and efiiciency. However, it is to be expressly understoodthat any type of oscillator circuit may be employed herein.

As mentioned heretofore, the present invention provides an oscillatorcircuit having novel means for producing and controlling a self-bias onthe control electrodes in such a manner as to generate radio frequencypulses having substantially rectangular symmetrical envelopes. As shownin Fig. 2, such means include the filter network 25 which takes the formof a low-pass filter network having a plurality of capacitance means 28and a plurality of inductance means 29 connected together inseries-parallel to form a filter network having a plurality of sections.For the purpose of the present invention the filter network need not besymmetrical and any number of sections may be included therein,depending upon the shape of the pulse envelope desired, as will appearmore fully hereinafter.

It has been found that when an electromotive force is applied to one endof a filter network of the above character that a voltage wave ispropagated down the filter toward the other end thereof from where thewave is reflected and returned to the end of the filter where the forcewas applied. While this action is taking place, a uniform current flowsinto the filter network, the value of which depends upon the surgeimpedance of the filter network and upon the internal impedance of theelectromotive force. Since the surge impedance of the network isconstant the voltage across the input of the filter is constant duringthe time the voltage wave is propagated from one end of the filter tothe other, or during the charging period of the filter, and the voltageacros the input of the filter abruptly doubles in value at the instantthe network is charged or when the reflected voltage wave arrives at theinput end of the filter. The time delay, or the time required tocompletely charge the filter, for a constant K fi lter disclosed, isapproximately equal to 1r/3\/LC per section, and that the total timebetween the application of an electromotive force and return of thereflected voltage wave is approximately equal to /3 N1r /LC, where N isthe number of sections, and L and C are the inductance and capacitancevalues, respectively, per section.

In view of th foregoing, it is to be expressly,

understood that the bias on the control electrodes and hence theelectrical angle through which the anodes draw current will be dependenton the internal impedance of the cathode electrode circuit, consideredas a self-biasing generator, and the surge impedance of the filternetwork. The surge impedance of the filter network is approximatelyequal to and it is preferred 'to properly select values of capacitancemeans 28 and inductance means 29 so that the ratio formed will producethe desired anode current angle and. to use the filter network alone forself-bias impedance. However, in some instances-it may vbe-desirable touse .a resistor 24., of a small value,in1 series between the controlelectrodev and the filter "to further provide selfbias. I

When a filter network of the foregoing. type .is inserted in. anoscillator circuit between. the control electrode. and the cathode, asshownin Fig. 2, the filter begins. to charge when oscillations commenceand holds the control electrode bias at a constant value during :a timeinterval equal to /3 N-n/IC, as discussed heretofore, and at the end ofsuch interval the sudden increase in voltage across the filter producesabias on the control electrodes of such value to block the tubes and tothus prevent the anodes from drawing current. Since the voltages are allconstant during the operating period the carrier freequency and'theoutput power are also constant.

The foregoing operationproduces pulse envelopes of substantiallyrectangular symmetrical shape, as shown in Fig. 3 of the drawings.

The pulse repetition rate is determined y the time required for thefilter to discharge through suitable bleeder resistors 30, and 3|,respectively connected in parallel to capacitance means 28 atoppositeends of the filter. Since the discharge of the filter network isordinarily relatively slow the discharge will be exponential incharacter with a period of discharge approximately equal to 1 Fair?)where R is the parallel value of resistance 30' and 3|. The repetitionrate may be synchronized with an external source by introduction of anelectrornotive force in series with the filter network, such astransformer 26 excited with an appropriate external, alternating currentsource 21, as shown in Fig. 2.

As shown in Fig. 4, the pulse repetition rate may be controlled by asynchronizing voltage introduced in parallel with the filter network byutilizing proper blocking impedances. In this embodiment, a. two tubetriode oscillator circuit is ance 24 included in such connection ifdesired, 1

and the lower terminal of the filter being connected to ground potentialat 32. A source of synchronizing voltage 21 is connected in series withthe filter with suitable blocking impedances which includes capacitance33, inductance 34 and resistance 35. Capacitance 33 serves to preventdischarge of the filter through the synchronizing system, whileresistance 35 tends to dampen any oscillations of the circuit. Theinductance 39 serves as a high impedance to the current surge andisolates the synchronizing system from the filter network during theperiod of the pulse. Inductance 39 is to be of such value to have anatural period ten times or more than the period of the pulse. Ifpreferred, the synchronizing system may be connected on the other sideof the filter.

In operation of the novel systems described heretofore, when electrondischarge devices I0 and II commence oscillating, rectified controlelectrode current is generated and flows to filter network 25. Whilefilter network is charging, the control electrodes are maintained at aconstarry bias determined by the surge impedance /L/C of the filternetwork and by the value of resistor .26. if employed, forapredeterminedperi- 0d of time approximately equal to 3 Nu/LC. The anodecurrent angle is established by the bias maintained on the controlelectrode, and since the bias is maintained constant the anode angleremains constant for the period N1r\/LC, and the oscillations generatedduring such period are symmetrical in form and of equal amplitude. Whenthe period. /3 N1r\/LC lapses, the voltage across the filter abruptlyincreases to a value substantially twice the constant value to increasethe bias. on the control electrodes a corresponding degree, thusblocking the tubes and preventing the anodes from drawin current. Sincethe tubes are abruptly blocked, theanode current angle necessarilyabruptly diminishes to an extinction point. The anodes will not againdraw current until the filter discharges through resistances 30. and 3|,the time for such discharge depending upon the value of the resistances,or may also be controlled by an external synchronizin source.

The foregoing operation produces radio frequency pulse envelopes of asubstantially rectangular symmetrical shape, as shown in Fig. 3. Sin e avoltage appearsfacross the filter and remains substantially constantthroughout a predetermined time. interval following theinitial'application of rectified control electrode current thereto, thepulse envelopes have substantially uniform magnitude throughout agreater portion thereof. Moreover, since the voltage rises rapidlyacross the filter after a lapse of. the predetermined interval of time,thus rapidly causing an increase of the bias on the control electrodes,the angle through which the anode draws current likewise rapidlydecreasesto an extinction point, thus causing the magnitude of the pulseenvelopes to sharply decrease from maximum to zero through a shortperiod of the pulse.

The present invention thus provides an oscillator circuit having novelmeans for providing and controlling a bias on the control electrodesincluded therein in such a manner to vary the angle through which theanodes draw current whereby radio frequency pulses having substantiallyrectangular symmetrical pulse envelopes are generated. The meansdisclosed is of such character that during the time \the radio frequencypulses are generated the carrier frequency remains substantiallyconstant, and that the means may be utilized in any self-quenchingoscillator circuit, and may be readily tuned to operate on any desiredfrequency.

Although only two embodiments of the invention have been disclosed anddescribed in detail heretofore, it is to be expressly understood thatvarious changes and substitutions may be made therein without departingfrom the spirit of the invention as Well understood by those skilled inthe art. Reference therefore will be had to the appended claims as adefinition of the limits of the invention.

The invention described herein may be manufactured and/or used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed is:

1. In an oscillator circuit for generating radio frequency pulses, anelectron discharge device having a cathode, anode and at least onecontrol electrode, means interconnecting said cathode, anode and controlelectrode in such a manner as to cause said device to oscillate wherebyrectified control electrode current is generated, and a filter networkcomposed of inductance and capacitance connected between said controlelectrode and said cathode for determining and maintaining, by theaction of said rectified control electrode current thereon, the angle ofthe plate current flow substantially constant throughout a period oftime following the initial flow of rectified control electrode currentthereto and thereafter for causing the angle of the plate current torapidly decrease to an extinction point.

2. In a radio frequency pulse generator, an electron discharge devicehaving a cathode, an anode and a control electrode interconnected insuch a manner so that said device generates radio frequencyoscillations, and means controlling generation of said oscillations insuch a manner that radio frequency pulses having ubstantiallyrectangular pulse envelopes are periodically produced, the last-namedmeans including impedance means for establishing a predetermined bias onsaid control electrode at the instant said device commences to generatesaid oscillations, said impedance means comprising inductance andcapacitance mean presenting constant impedance to the flow of rectifiedelectrode current therethrough and thus maintaining said bias at saidpredetermined value for a period of time equal to the charging time ofsaid capacitance means and thereupon abruptly varying said impedance andsaid bias to abruptly render said device nonoscillating, and resistancemeans associated with said impedance means for controlling the dischargeof said capacitance means whereby said device is maintained in anon-oscillatin state for a second predetermined period of time.

3. In a radio frequency pulse generator, an electron discharge devicehaving a cathode, an anode and a control electrode interconnected insuch a manner so that said device produces radio frequency oscillations,and a filter network electrically connected to said device forcontrolling eneration of said oscillations in such a manner that radiofrequency pulses having substantially rectangular symmetrical pulse'envelopes are periodically produced, said filter network having apredetermined impedance value for establishing a, predetermined bias onsaid control electrode at the instant said device initiates generationof said oscillations, and comprising inductance and capacitance meansinterconnected in such a manner as to maintain said impedance value andsaid bias constant for a period of time equal to the charging time ofsaid capacitance means and thereafter for abruptly varying saidimpedance value and said bias to abruptly terminate generation of saidoscillations, and a source of synchronizing voltage connected inparallel with said filter for controlling the discharge of saidcapacitance means.

4.In a radio frequency pulse generator, an electron discharge devicehaving an anode, a cathode and a control electrode interconnected insuch a manner that said device generates radio frequency oscillations,and means controlling the operation of said device in a manner to causeit to produce a series of pulses havingsubstantially rectangularsymmetrical envelopes, said means comprising a transmission lineconnected in bias controlling relation to said control electrode, saidtransmission line being terminated to produce reflection of a voltageimpressed upon it, in such phase as to increase the bias on said controlelectrode to render said device non-conducting, the delay time of saidline being longer than the period of said oscillations.

ARTHUR A. VARELA.

